1. Field of the Invention
This invention generally relates to sensor technology and more specifically to wireless temperature calibration devices and methods for semiconductor device thermal fabrication processes.
2. Description of the Related Art
Numerous semiconductor device thermal fabrication processes employ temperature sensors which require calibration against reliable and repeatable standards. An important group of device fabrication processes is rapid thermal processing (RTP). Most of the RTP reactors employ non-contact pyrometry for wafer temperature measurement and control, as shown in FIG. 1. However, the accuracy and repeatability of RTP temperature measurement by pyrometry depend strongly on the wafer emissivity. In practice, frequent pyrometry sensor calibrations are required in order to obtain acceptable process repeatability. These frequent cross-calibrations are usually performed by placing separate standard calibration wafers with bonded thermocouples (TC-bonded wafers) in the process chamber, as shown in FIG. 1. The TC-bonded calibration wafers are placed in the process chamber between a quartz window and a gas showerhead. However, the TC-bonded calibration wafers require external electrical connections to the TC wires. As a result, the calibration process needs manual loading and unloading of the TC-bonded wafer. This manual process is time consuming and is not suitable in a semiconductor device manufacturing environment due to its detrimental impact on equipment utilization. This problem is even more severe when TC-bonded wafers with multiple distributed thermocouples are required for calibration of multi-point pyrometry sensors housed in a multi-zone illuminator. In addition, thermocouple-assisted temperature calibrations are not suitable in reactive (e.g. oxidizing) ambients at higher temperatures (&gt;950.degree. C.). This is due to the fact that the thermocouple junctions degrade rapidly under these conditions. Even under inert conditions, thermocouples have limited lifetime. Thus, TC-bonded wafers exhibit limited lifetime and can only be used for a limited number of manual calibration runs. TC-bonded wafers may also introduce calibration errors (of as much as 10.degree. C. or larger) due to the localized temperature offset caused by thermal loading. Special bonding procedures are required to minimize the sources of calibration error. Commercial TC-Bonded wafers are available for temperature sensor calibrations; these TC-bonded wafers are, however, expensive. Finally, the manual thermocouple-assisted calibrations may introduce contaminants into the process chamber. This can reduce the device manufacturing yield, particularly in critical processes such as gate dielectric formation and epitaxial silicon growth.